1. Field of the Invention
The present invention relates to olefin polymerization catalysts and methods of producing and using the catalysts, and more particularly, to silica supported olefin polymerization catalysts prepared from mixtures of transition element compounds and organometallic compounds.
2. Description of the Prior Art
It is known to polymerize .alpha.-olefins and mixtures thereof at low pressures with coordination catalysts prepared from mixtures of transition element compounds and organometallic compounds.
In the polymerization of ethylene and propylene, it is desirable to perform the polymerization reaction in an inert diluent at a temperature at which the resulting polymer or copolymer is relatively insoluble in the reaction medium. Also, it is desirable that the polymer so produced does not require additional processing to remove catalyst residue therefrom. In order to achieve the foregoing, a polymerization catalyst must be employed which is capable of producing polymer in a high productivity whereby the residual catalyst level in the recovered polymer is maintained at a very low level. It is also desirable that the catalyst bring about the production of polymer particles which are characterized by strength, uniformity of size, and a relatively low level of fine particulate material.
Olefin polymerization catalysts of the type described above prepared from mixtures of transition elements and organometallic compounds have been developed and utilized which achieve, in varying degrees, the desired results described above. For example, U.S. Pat. No. 4,394,291 issued July 19, 1983 discloses an olefin polymerization catalyst prepared by reacting a metal dihalide with one or more transition metal compounds and reacting that product with a certain organoaluminum compound. The resulting catalyst, with or without a cocatalyst, achieves high enough productivity that catalyst residue contained in the produced polymer is low enough to not significantly affect the polymer properties.
U.S. Pat. No. 4,719,271 issued Jan. 12, 1988 discloses a polymerization catalyst similar to that described above, i.e., a catalyst prepared by reacting a metal dihalide with a transition metal compound and reacting that product with an organoaluminum compound. The catalyst is prepared in the presence of a particulate diluent, e.g., polymeric fibrils.
U.S. patent application Ser. No. 07/284,280 filed Dec. 14, 1988 and assigned to the assignee of this present invention discloses yet another coordination catalyst prepared by contacting a soluble complex produced by contacting a metal dihalide with a transition metal compound in the presence of particulate silica. The resulting silica supported complex is contacted with an organoaluminum halide to produce a high activity olefin polymerization catalyst.
Thus, there has been and continues to be a search for catalysts useful in the polymerization of .alpha.-olefins which result in high polymer productivity and produced polymers having high strength, a uniformity of size, and a relatively low level of catalyst residue therein. By the present invention, improved silica supported high activity olefin polymerization catalysts, methods of producing the catalysts and methods of using the catalysts are provided which achieve superior results in the above described areas.